Many animals change their skin colors to communicate, to express mood, for camouflage, or to respond to environmental changes1-3. In the tissues of these animals, various nano and microscale components play roles in generating distinct colors and achieving rapid color changes4,5. Inspired by nature, sensors are being developed that change color in response to target chemicals by employing biomimetic structures and mechanisms. In particular, structurally colored biomaterials, such as butterfly wings, beetle exocuticles, cephalopod skins, mammalian skins, and avian skins/feathers6-14, provide insight into developing colorimetric sensors. These materials exhibit brilliant colors that are derived from their hierarchically organized structures and are resistant to photobleaching7. Furthermore, they can rapidly shift colors upon exposure to chemical vapors due to structural and/or refractive index changes15. Therefore, both structurally colored materials in nature and their synthetic analogues are being explored as simple and portable colorimetric sensor platforms16-21.
A significant drawback of previous structural color sensors is their limited intrinsic affinity for specific targets of interest (e.g., explosives and pathogens) and resulting poor selectivity against analytes with similar chemical structures. Current methods to promote target specificity by either chemically incorporating specific recognition motifs or by synthesizing arrays of cross responsive platforms for “artificial nose” type pattern recognition are promising19,22-24, but incorporating analyte-responsive elements into the sensing devices is still challenging because it requires complex designs and multistep synthetic pathways. Furthermore, many structurally colored sensors exhibit viewing-angle dependent color changes (iridescence) that may complicate analysis.